The present invention is a flame retarded thermoplastic resin composition containing an intumescent flame retardant.
Although flame retarded thermoplastic resin compositions are known, it is usual to use intumescent fire retardants which require synergists, for sufficient effect to be useful. Intumescent nitrogen-phosphorus fire retardant systems have been used for many years. The systems have the potential benefits of low smoke and of being halogen free. They are typically based on phosphate salts and synergists. The synergists include polyhydric and nitrogen containing compounds. Various synergists and their precursors have been developed for specific applications and the identification and selection of synergists remains an area of active work due to potential benefits of a high performance product capable of meeting stringent processing, physical property and smoke corrosivity standards and a number of patents have been issued over the last ten years which describe the use of these fire retardants in thermoplastic and mastic applications. Among these patents are U.S. Pat. Nos. 4,694,030; 3,485,793; 3,442,849; 4,727,102; 4,174,343; 4,104,073; and French Patent No. 2 367 302. In general, types of resins and these uses are well known (see for example U.S. Pat. No. 4,174,343 and 4,727,102).
Although useful in fire retarding some polymer systems, known intumescent fire retardants have disadvantages which limit their use. The present invention provides an intumescent system which avoids disadvantages of the known intumescent fire retardants to provide useful compositions.
One disadvantage of the known intumescent fire retardants is that the known fire retardants impart a variety of performance problems and other deficiencies to the resin composition. These problems can limit or eliminate their usefulness with some resins and in particular, polyolefins. Off-gassing and liquid bleed out in particular have been found in these systems and these disadvantages are believed to have been caused by phosphate salt/synergist interactions.
The present invention provides a new intumescent fire retardant which does not require the use of synergists in order to provide sufficient effectiveness.